The dimensions of the medals are specified as a minimum of 60mm diameter by 3mm thick. For a cylinder, that's 8.482 cm^3 volume per medal, minimum. The 2020 Olympics has 339 events, each with a gold, silver, and bronze medal. Market price I found for gold as of this post is $58.56/g and silver is $0.82/g. Gold has a density of 19.30 g/cm^3 and silver 10.49 g/cm^3. I'm not keeping track of sig figs because I don't care enough for a quick rundown.
For the gold medal, its composition is listed as minimum 92.5% silver with 6g of gold mixed in. I didn't see what the percentage specified (mass, volume) so I'll assume volume for silver henceforth. 7.845 cm^3 is 92.5% of min volume of a medal. This works out to 82.294 g of silver (7.845 cm^3 * 10.49 g/cm^3). Using market prices above, silver value: $67.48, gold value: $351.36, total materials value: $418.84.
Now, if the gold medal were solid gold, you'd have 163.703 g (8.482 cm^3 * 19.3 g/cm^3) of gold. Materials market value of the medal would be $9,586.
For the silver medal, it's 92.5 silver with nothing specified mixed in. So the identical silver component from the gold medal which means its total materials value is $67.48.
If the silver medal was pure silver, we'd have 88.976 g (8.482 cm^3 * 10.49 g/cm^3) and the materials value would be $72.96.
The bronze is 97% copper, 0.5% tin, and 2.5% zinc. I won't do this because I'm not interested, I'll leave it as an exercise for the reader.
Now the fun part, rough estimate of total material cost of existing gold and silver medal compositions for all 339 events: $164,862.48 (339 * ($418.84 + $67.48)).
Rough material cost if the gold medals were actually gold and the silver were actually silver: $3.274 million (339*($9,586 + $72.96). It would cost about 20x the current material costs to give the athletes more representitive and valuable medals. The total cost of this would be an additional ~$3.1 million to the host or whoever pays for it.